X-ray apparatus



Juy 30, 1935. D. H. sLoAN 2,009,458

X -RAY APPARATUS JIlly 30, 1935. D. H. sLoAN X-RAY APPARATUS Filed Nov. 27, 1935 5 Sheets-Sheet 2 July 30, 1935. D SLOAN 2,009,458

X-RAY AEPABATUS Filed Nov. 27, 1935 3 Sheets-Sheet 5 ATTR YS.

Patented July 30, 1935 UNITED STATES X-BAY APPARATUS David H. Sloan, Berkeley, Calif., assigner to Research Corporation, New York, N. Y., a corporation of New York Application November 27, 1933, Serial No. 699,833 8 Claims. (Cl. Z50-3 5) This invention relates to improvements in X- ray apparatus and the main object of the invention is to provide for production of extremely hard X-rays by the application of very high voltage to the electrodes of the apparatus. A further object of the invention is to provide for supply of suiicient electrical energy together with suiiiciently high voltage, to the X-ray-producing electrodes to cause the production of X-ray or Roentgen rays of great energy orl intensity as well as hardness.

A further object of the invention is to provide an X-ray apparatus of the character above referred to; having means for increasing the electron emanation from the cathodes in a convenient and practicable manner.

A further object of the invention is to so control the passage of electrons from the cathode to the anode, in an X-ray apparatus, as to eliminate or minimize the production of relatively soft rays,

This application is a continuatiomin-part of my copending application Ser, No. 604,642, filed April 11, 1932.

I'he accompanying drawings illustrate my invention and referring thereto:

Fig. 1 is a vertical section of a typical form of my invention, the electrical energizing connections therefor being shown diagrammatically, said section taken on line I-I in Fig. 3;

Fig. 2 is an enlarged sectional view on line 2 2 in Fig. 1;

Fig. 3 is a sectional View taken on line 3-3 in Fig. l;

Fig. 4 is an enlarged view of the inductance or resonance coil partly broken away;

Fig. 5 is a partial elevation of a modied form of the inductance or resonance coil with the electrical energizing connections therefor:

Fig. 6 is a broken elevation of another modied form of the inductance or resonance coil;

The apparatus shown in Figs. 1 to 3 comprises a casing, chamber or container I, a coil 2 within said chamber and supported at one end on a wall of said chamber and having an electrode 3 at the other end, an electrode 4 within said chamber opposing the electrode 3, and means for producing high frequency oscillating current in said coil in such manner as to generate high voltage between the electrodes 3 and 4. Chamber I is evacuated, for example by a connection 5 leading to suitable exhausting means, a refrigerating means such as a liquid air receptacle 5 being provided for such connection so as to facilitate the evacuating action. In the drawings the coil 2 is supported on the top of the chamber I, but

it will be understood that it may be supported on and extend from the bottom or the side walls of the chamber. The free end of coil 2 and the anode 3 carried thereby are effectively insulated from the wall of the casing by the evac- 5 uated space therebetween so that, by maintaining suiiiciently high vacuum within the casing,

an extremely high oscillating voltage may be maintained at said anode.

Chamber I is mounted on suitable supports 6 `10 and is shown as cylindrical and provided with a top wall 6a and removable bottom or closure member 'I, normally held in closed position by counterweights 8 connected to member 'I by iiexible connections 8a passing over pulleys 9, the joint between member 1 and the bottom of the side wall of casing I being sealed, for example by wax, indicated at I0.

If desired a window Ia may be provided in the wall or casing I said window being of glass or of suiiicient thinness or of sufficiently low density metal to facilitate passage of X-rays from the anode 3 to the outside of the casing. However, by suitably designing and adjusting the apparatus and its supply connections it is possible to provide X-rays or Roentgen rays of such extreme hardness that such rays can penetrate without dilculty the walls of the casing or container I when such Walls are made, for example, of steel of suiicient thickness to withstand the atmospheric pressure from the o utside; it being only necessary in that case to fill or protect all parts of the casing except the part in the direct path of the X-rays from the anode by a suitable covering or enclosure of lead or equivalent material as above mentioned so as to confine the X-ray radiation from the apparatus to any desired portion of the wall of said casing.

Coil 2 is provided with passage means for circulating cooling medium (such as water, oil, air, et cetera) therethrough, said coil being formed, for example as a tube II of copper or other conducting material bent to form a coil or helix `(see Fig. 4), and an inner tubeA IIa, of soft rubber, for example, extending within the coil tube II from the supported end to near the other end thereof, and communicating adjacent said other end, with the outer tube, so as to form passage means extending from the said supported end of coil tube II to the other end thereof and then back to the supported end thereof. Pipe connections I2 and I3 are connected respectively to the coil tube I I and with the inner tube I I a and are connected to any suitable means for delivering and receiving cooling iiuid, so as to provide for circulation of such uid through the said passage means and thereby prevent undue heating of the high voltage generating coil. The coil 2 is provided, at the end thereof which is remote from the supported end, with a. hollow electrode 3 and the coil tube II and inner tube IIa open into the cavity or passage I5 within said electrode so as to circulate cooling medium through said electrode.

Any suitable means may be employed for producing high frequency oscillations in the coil 2. I prefer to employ energizing means as shown in Figs. 1 and 4 comprising a coil member I6, which may be a partial turn co-axial with the turns of coil 2, and placed within chamber I, in inductive proximity to coil 2, and suitable oscil lation circuit means connected to said coil member. It is desirable to provide coil member i6 with means for preventing undue heating thereof and for this purpose said coil member may be formed as a tube connected at its respective ends to inlet and outlet connections I8 and I9 for cireulating a cooling medium such as water therethrough. In order to enable production of the necessary high oscillating potential at the respective ends of the coil member I6 it is desirable to provide suitable high resistance connections between the ends of the coil member and the said inlet and outlet connections i and I9, and such high resistance connections may comprise tubes 26 and 2i of insulating material such as rubber hose, the circulating water or other iiuid of suitable high resistance being contained within said tubes. By making the tubes 20 in the form of coils of great length, the resistance of the column of liquid may be made sufficient to prevent undue leakage from the ends of the coil member i6, it being understood that if extremely high resistance is required pure water may be used, circulated from a special receptacle.` In some cases however ordinary water from a service main may be employed.

The oscillation circuit means for energizing the coil member I6 is shown as of the push-pull type and as fed by a transformer or auto-transformer 22 connected to the plate circuit of the pushpull circuit. For example as shown, the grids of the 3 electrode tubes 24 and 25 of the push-pull circuit may be connected to opposite ends of an inductance means 2'I having its midpart connected through balanced capacity and induction reactance means indicated at 28 to ground and to the lament side of the plate circuit for each tube, the grids being thereby coupled to the plate circuit so as to receive energy therefrom and cause production of oscillations in the plate circuit. The'plate connections for the respective tubes are connected by wires 30 and 3| to the respective'ends Ia and IGb of coil member I8 and said ends are suitably insulated from the casing upper wall 8a as by means of insulators I'I so that when high frequency oscillations are set up in the push-pull circuit the respective ends of the coil I8 are given high frequency oscillations of reverse potential and corresponding high frequency current is thereby produced in said coil member. The spacing of coil member I6 with reference to the coil 2 is such that the oscillation currents produced in coil member i6 cause production of high frequency oscillations in coil 2 and of an oscillating high voltage at the end of said coil 2 which is remote from the supported end thereof.

The energy supply line 38 from the transformer 22 preferably includes inductance means 3l and is connected to ground at the transformer end of the inductance through a condenser 36, to prevent feed back of high frequency oscillations from the oscillatory circuit.

A shield is preferably provided about the oscillatory circuit means as shown in dot-dash lines at 39, and the above-mentioned ground connection is preferably made within this shield, so that high frequency radiations are substantially pre- Vented from escaping from the apparatus.

In case alternating current is used for energizing the oscillation circuit it is desirable to provide means for absorbing the energy of the half- Wave of the alternating current which is not utilized in energizing the coil I6, it being understood that the thermionic devices 24 and 25 operate selectively to utilize only that half-wave,

of the alternating current which produces the A.negative potential at the filament electrodes thereof and as it is necessary to provide for high energy delivery during the half-Wave so utilized it is also necessary to provide for absorption of the energy during the other half-wave in order to prevent undue and possibly injurious rise of potential during such other half-wave. For this purpose circuit means may be provided comprising a two-electrode thermionic tube or electric valve 34 connected in series with a resistance 35 across the output leads of supply transformer 22. When rectified current is used for energizing the oscillation circuit supplying the coil I6, this auxiliary energy-absorbing circuit may be eliminated.

If the transformer 22 is designed to give sufcient power on the useful half-cycle without producing a high enough voltage to damage the oscillator tubes and associated equipment during the unused half-cycle, 1this energy-absorbing circuit is unnecessary. This latter arrangement has been found quite satisfactory.

Suitable electrode means are provided opposing the electrode means 3 aforesaid. In Fig. 1 the said opposing electrode means is shown as a thermionic element or hot iilament cathode 4 having energizing connections 4I and 42. With an apparatus of the character above described it is practicable to produce electrical potential difference between the electrodes 3 and 4 which is so great that it becomes desirable in some cases to limit eiective emission of electrodes from the cathode. For this purpose a shield tube 43 of conducting material, mounted on but insulated from casing I, may! be provided around the cathode and is given a negative bias with reference to the cathode for example by giving a positive bias to the cathode itself, as indicated, so that an electrical field is produced between the cathode and the said shield tending to hold back any emitted electrons except When the anode is suiciently positive for its field to overcome this negative bias field at the more exposed parts of the lament surface. Thus electrons are emitted only when the anode is highly positive and as a resultl of their bombardment of the anode the X-rays produced thereby will be chiefly hard rays and the waste of energy and undue heating due to emission of electrons of relatively low velocity will be done away with. It will be understood that to produce such restricted emission of electrons from the cathode it is necessary that the dominant electrical field produced between the electrodes 3 and 4 by the combination of the oscillatory field and bias eld must be positive enough to overcome the space charge of the rev sultiugelectrony emission fo'r themost positive portion of theA high frequency cycle.

Any suitable means may be used to energize cathode member or filament 4 and to give a suitable bias thereto. For example, said cathode filament may be connected by wires 4I and 42 to a low-voltage transformen", to supply the current necessary to raise the cathode filament to incandescence, and the cathode 4 and shield 43 are connected respectively by wires 40 and 43 to a suitable source of unidirectional high voltage, said wires being for example connected to the second-v ary of Aa high voltage transformer 50, a suitable rectifier or electric valve being included in the connection. The cathode member is grounded as shown at 52. If desired, an ammeter may be included in the filament circuit, as shown at 44.

The push-pull circuit comprises two tuned-grid tuned-plate oscillators side by side and 180 out of phase, (see Radio Engineering" Terman, Mc- Graw-Hill Book Co., Inc., N. Y., 1932, page 245) One oscillator circuit includes part of inductance 21, the plate-filament capacity coupling in tube 24, and part of coil member I6, and the other oscillator circuit includes the other parts of inductance 21 and coil I 6 and the plate-filament capacity coupling in tube 25.

From the secondary of transformer 22, alternating voltage is applied to the respective tubes 24 and 25, and during periods in which the plate potential is positive, current will flow from said secondary through wire 38 and choke coil 31 to each plate and thence through the filament and ground back to the secondary. oscillations will then be set up in the respective push-pull oscillator circuits in the usual manner of operation of such circuits, such circuits being fed by energy i supplied through the plate-grid capacitive couplings in the respective tubes. With filament and plate voltages applied, some slight disturbance will cause one grid to become more positive than it had been. This draws more plate current and lowers the plate voltage of that tube because of the drop across the impedance of the load circuit. The circuits are so adjusted that midpoint of the balanced push-pull load (namely, the coil member I6) stays at constant potential, hence the second anode potential is raised as much as the first one is lowered. As the energy of the grid disturbance is expended, the first grid becomes more negative, reducing its plate current and causing its anode potential to rise. Simultaneously the second grid goes positive, and increases its plate current, de-V creasing its plate potential just a half cycle after the corresponding action of the rst tube. This process increases in intensity until the amplitude of oscillation is limited by the grid and plate direct potentials and by the tube and circuit impedances. Grid potential (bias) is most easily obtained by the voltage drop across a grid leak resistance (indicated at 28), caused by the flow of electrons which are picked up by the grids during the part of the cycle in which they are positive with respect to the lament.

By suitably proportioning the electromagnetic coupling of inducing member I6 with relation to the resonance coil 2, and supplying oscillating current of suitable voltage and frequency to the coil member I6 by the means above-described, it is practicable to produce between anode 3 and cathode member 4 a potential difference of more than 75 times the voltage impressed in coil member IE. Thus, with 15,000 volts oscillating current impressed on coil member I6, which may require anapplcation of 20,000 or more volts to the oscillator tubes, an oscillating voltage otmore than 1,000,000 may be produced at the anode I: the cathode member 4 being grounded. This voltage is effective, during the half-waves when the member 31s positive, in producing acceleration of electrons toward the anode member 3 so as to produce X-rays of extreme hardness, such rays passing through the wall of the casing or through the window -I a in such wall, as above described, for utilization in any suitable manner.

Various modifications may be made in the apparatus above-described without departing from my invention. 'Ihus as shown in Fig. 5 the lnductance coil shown at 2a may be energized by direct connection of a portion thereof to the oscillation circuit shown at 60, the output of said oscillation circuit being connected to a portion 2b of said inductance coil, which is so proportioned in length to the length of the whole coil as to provide the requisite multiplication of voltage at the free end of the coil.

In order to provide return circulation of the cooling medium within the inductance coil any suitable construction may be used provided for outgoing and return passages. Thus the coil may be provided with inner and outer tubes as shown in Figs. l, 4 and 5 or it may be composed of two tubes extending side by side as shown at 62 and 63 in Fig. 6. In order to insure that the cooling action of the fluid shall extend effectively to the outer end of the resonance coil, the tube or means l la for separating the incoming from the outgoing fluid is preferably made of heat insulating material, the softrubber tubing above referred to being suitable for that purpose.

In the operation of the apparatus, high frequency oscillations are generated in the inductance coil 2, resulting in alternating high voltage at the free or outer end of said coil; and during the half-waves that the potential at the electrode 3 at said free end of the coil is positive electrons will pass from grounded electrode 4 (operating as cathode) to electrode 3 (operating as anode) and X-rays are produced by the impact of such electrons on electrode 3 which operates as an anticathode for effective emission of X-rays. Electrode 4, operating as the source of electrons, is raised to suitable temperature by the electrical current supply means described, so as to provide for thermionic emission in any desired amount, and said electrode is maintained at a suitable electrical bias to restrict the passage of electrons so that the bombardment of electrode 3 is limited to electrons having high velocity and correspondingly high energy, whereby hard X-rays are produced at electrode 3 and the production of relatively soft X-rays is substantially prevented.

The fact that the electrode 3 and the adjacent end of coil 2 are insulated from the grounded casing by the evacuated space within the casing, enables extremely high voltages to be produced between electrode 3 and grounded electrode 4, resulting in the production of X-rays of extreme hardness and energy intensity, and the fact that electrode 4 operating as the cathode, is grounded, enables the thermionic element thereof to be supplied with the necessary current without the complications that would be necessitated if the high potential electrode were made the cathode, this advantage being particularly important .in view of the necessity for cooling the high potential electrode and its supporting and energizing coil, by means of circulating fluid. y

I claim:

1. Apparatus for producingX-rays, comprising an evacuated casing, having grounded connection, a coil supported at one end within said casing and having its other end substantially free, so as to be insulated from the casing by the evacuated space between said free end and the wall of the casing. an anode at said free end of the coil, said anode operating as the anticathode for emission of X-rays means for inducing high frequency electricai oscillations in said coil to produce oscillating high voltage at said anode, a cathode mounted in the casing opposite'said anode, said cathode comprising a thermionic element having a grounded connection and energizing means for said thermionic element.

2. A construction as set forth in claim l and comprising, in addition, conducting means adjacent the cathode and means for maintaining negative potential at said conducting means, to produce a negative bias in the electrical eld adjacent said cathode and thereby prevent passage from the cathode to the anode of electrons of low velocity.

3. A construction as set forth in claim 1 in which said coil is provided with internal passage means for circulating cooling uid from the supported end of'the coil to the free end thereof and back to the supported end.

4. A construction as set forth in claim l in which the coil and the anode thereon are provided with passage means and means are provided for circulating cooling liquid from the supported end of the coil to and through the anode at the free end thereof, and back to the supported end.

,5. A construction as set forth in claim l in which said coil is provided with internal passage means defining ingoing and outgoing passages for circulating cooling uid from the supported end of the coil to the free end thereof and back to the supported end, said passage means comprising heat insulating means for separating the ingoing from the outgoing passages.

6. Apparatus for producing X-rays comprising an evacuated casing, a coil within and supported at one end upon said casing, a target at the other end of said coil for emitting X-rays, passage means extending from the supported end of said coil to the other end thereof and back to the supported end, inlet and outlet means adjacent said supported coil end for passing a cooling medium through said passage means, means for producing high frequency oscillations in said coil, and cathode means opposing said target, said target being hollow and communicating with said passage means for circulation of the cooling medium through said target.

7. In apparatus for producing X-rays, an evacuated casing, a coil supported at one end within said casing and provided with a hollow target at its other end, said coil being formed as a tube of conducting material, a tube within said coil tube and forming therewith passage means extending from the supported end thereof to the interior of said hollow target and back to the supported end of the coil tube, inlet and outlet connections for said passage means for circulating a cooling medium therethrough, and cathode means mounted opposite said hollow target.

8. A high voltage apparatus comprising an evacuated chamber, an oscillation coil within said chamber' and supported at one end on the wall of the chamber, the other end of the coil being free of mechanical connection with the wall of the chamber and being insulated from said Wall by the evacuated space between the free end of the coil and said wall, said other end of the coil being provided with a target, cathode means mounted within said chamber and opposing said target, and means for applying high frequency alternating voltage to a part of the coil adjacent the supporting end thereof, said coil being provided with passage means extending from the supported end of the coil to the other end thereof and thence back to the supported end, and inlet and outlet connections at the supported end of the coil for passing cooling medium through said passage means, said target being hollow and being connected with said passage means so that the same cooling medium which cools the coil also serves to cool the target.

DAVID H. SLOAN. 

